Porsche began experimenting with turbocharging technology on their race cars during the late 1960s, and in 1972 began development on a turbocharged version of the 911. Porsche originally needed to produce the car in order to comply with homologation regulations and had intended on marketing it as a street legal race vehicle like the 1973 Carrera 2. 7 RS. The FIA's Appendix “J” rules upon which the 911 Turbo Carrera RSR 2. 1 was entered into competition in 1974 changed in 1975 and 1976. The FIA announced that cars for Group 4 and Group 5 had to be production cars and be available for sale to individual purchasers through manufacturer dealer networks. For the 1976 season, new FIA regulations required manufacturers to produce 400 cars within a twenty-four month period to gain approval for Group 4. Group 5 would require the car to be derived from a homologated model in Group 3 or 4. Porsche's Group 4 entry was the 934, homologated on 6 December 1975. For Group 5, Porsche would develop one of the most successful racing cars of the time, the 935. The 911 Turbo was put into production in 1975. While the original purpose of the 911 Turbo was to gain homologation for the 1976 racing season, it quickly became popular among car enthusiasts. Four-hundred cars were produced by the end of 1975.  Since Porsche wanted to compete in the 1976 season, they gained FIA homologation for the Porsche Turbo for Group 4 in Nr. 645 on 6 Dec 1975 and the 1,000th 911 Turbo was completed on 5 May 1976.